Acanthamoeba is a genus of amoeba most commonly found in most soil and water habitats and can form metabolically inactive cysts which are resistant to desiccation, temperature fluctuation from −20 to 56° C., and most disinfectants at working concentrations. It can cause acanthamoeba keratitis, a painful, potentially-blinding infection of the cornea. Acanthamoeba keratitis is often associated with trauma to the cornea and with contact lens wear as a result of poor lens care and hygiene.
It has been reported that hydrogen peroxide-based lens care solutions can be effective against the resistant cyst form of Acanthamoeba when being used at a concentration of 3% with an exposure time of at least 4 to 6 hours. See, S. P. Johnston et al., “Resistance of Acanthamoeba cysts to disinfection in multiple contact lens solutions,” Journal of clinical microbiology, vol. 47, no. 7, pp. 2040-5, July (2009); R. Hughes & S. Kilvington, “Comparison of Hydrogen Peroxide Contact Lens Disinfection Systems and Solutions against Acanthamoeba polyphaga,” Antimicrobial Agents and Chemotherapy, vol. 45, no. 7, pp. 2038-2043, July 2001. However, hydrogen peroxide in these lens care systems is toxic to the cornea and thereby must be neutralized before lenses can safely be worn by a patient. Hydrogen peroxide typically is neutralized by adding a catalyst either during the disinfection process (i.e., one-step involving use of a platinum-coated disk or soluble catalase tablet) or afterward (i.e., two-step involving the addition of a catalase or a reducing agent after a designated disinfection time), for example, as described in patents and published patent applications U.S. Pat. Nos. 4,585,488, 4,748,992, 4,899,914, 5,011,661, 6,440,411, 5,089,240, 5,196,174, 5,275,784, 5,468,448, 5,558,846, 5,609,264, 5,609,837, 5,958,351, 6,945,389, 4,812,173, 4,889,689, 5,523,012, 5,576,028, 5,807,585, 5,462,713, 5,591,397, 5,312,586, US 2011/0114517, and EP0124461 (herein incorporated by references in their entireties). The study of Hughes and Kilvington indicated that the commercially available hydrogen peroxide-based, one-step lens care systems has low or no activity against the cysts of Acanthamoeba species under study because of insufficient exposure time, whereas the commercially available two-step systems can have at least a 3-log kill after 4 hours of exposure. However, one disadvantage associated with the use of a two-step system is that a patient may inadvertently fail to neutralize hydrogen peroxide or prematurely remove lenses from the system, thereby suffering pain and trauma caused by hydrogen peroxide introduced into the eye.
WO 2013056165 describes a complicated lens cleaning system which functions as a two-step hydrogen peroxide system while, for the user, it functions as a one-step system. A system of WO 2013056165 comprises a reservoir for holding a hydrogen peroxide solution, a complex base that is coupled to the reservoir to ensure a hermetically closed reservoir environment and has a first and a second segment, a lens holder assembly configured to locate and releasably coupled lenses within the reservoir and being coupled to the first segment, and a drive mechanism being coupled to the second segment and configured to selectively introduce a catalyst to the hydrogen peroxide solution.
U.S. Pat. No. 4,836,859 describes a method for treating contact lenses with hydrogen peroxide involving electrochemically decomposing and removing the remaining hydrogen peroxide. However, this patent fails to address issues associated with electrolysis of hydrogen peroxide solutions, such as, for examples, pH changes, by-products (e.g., chlorine, hypochlorite, etc.) of electrolysis of hydrogen peroxide solution, etc.
U.S. Pat. No. 5,225,055 describes an aqueous solution for use in electrochemical cleaning and disinfecting contact lenses, which comprises hydrogen peroxide, a blend of sodium chloride (as a first ionizable salt) and second ionizable salt including a metal of Group IA or IIA of the Periodic Table.
U.S. Pat. No. 5,302,345 describes a method of and apparatus for generating superoxides and other free radicals for cleaning and sterilizing contact lenses, tonometers and other poorly oxidizing objects in an electrolytic solution which may optionally include an antiseptic such as hydrogen peroxide, enzymes and soaps and for neutralizing the above agents by using electrolysis to decompose the peroxide and to generate free radicals that neutralize the enzymes and soaps and sterilize. However, this patent does not address the left-over free radicals generated for neutralizing the enzymes and soaps and for sterilizing lenses.
Thus, there is still a need for a simple lens care systems which can have microbial efficacy toward a broad spectrum of organisms including Acanthameoba. 